Controlled electroless plating

ABSTRACT

An electroless metal deposition process to make a semiconductor device uses a plating bath solution having a reducing agent. A sample of the bath solution is taken and the pH of the sample is increased. The hydrogen evolved from the sample is measured. The hydrogen evolved is used to determine the concentration of the reducing agent present in the sample. Based on the determined reducing agent concentration, the plating bath solution is modified.

This application is a Divisional of U.S. Ser. No. 10/994,720, filed Nov.22, 2004.

CROSS REFERENCE TO RELATED APPLICATION

This application is related to pending U.S. patent application Ser. No.10/650,002 filed by Mathew et al. entitled “Semiconductor Process andComposition for Forming A Barrier Material Overlying Copper”, filed Aug.27, 2003 and now assigned to the assignee hereof.

FIELD OF THE INVENTION

This invention relates generally to semiconductors, and morespecifically, to making semiconductor devices having very smalldimensions.

BACKGROUND OF THE INVENTION

Semiconductor processing typically involves the deposition of a metallayer. One known technique to deposit metal in semiconductors is viaelectroless deposition that utilizes bath solutions to form the metal.It is critical that the concentration levels of the bath solutioncomponents be maintained within certain acceptable concentration limits.Equipment has been developed to accurately measure the concentration ofbath solutions components to generate a bath solution of desiredproperties. However, as the electroless deposition process occurs, theconcentration of various components decreases and byproducts aregenerated. For some applications, such as electrolytic plating ofnon-electronic products, additional component materials may be added toreplenish depleted components. However, for semiconductor manufacturinginvolving small dimensions of metal deposition, component compositionprocess limits are much more critical. Therefore, electroless bathsolutions typically have a limited amount of useful application and aretypically discarded once a certain amount of use or a certain amount oftime has occurred. The proper disposal of bath solutions is an expensiveand time consuming aspect of semiconductor manufacturing.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and not limitedto the accompanying figures, in which like references indicate similarelements.

FIG. 1 illustrates in cross-sectional form a semiconductor device havinga metal component that has been deposited;

FIG. 2 illustrates in cross-sectional form further processing of thesemiconductor device of FIG. 1;

FIG. 3 illustrates in perspective view an electroless metal depositionsystem in accordance with the present invention;

FIG. 4 illustrates in graphical form the relationship between thequantity of evolved hydrogen and reducing agent concentration in a bathsolution;

FIG. 5 illustrates in perspective view a first embodiment of a portionof the analysis module of FIG. 3;

FIG. 6 illustrates in perspective view a second embodiment of a portionof the analysis module of FIG. 3; and

FIG. 7 illustrates in flowchart form a process control methodology forelectroless metal deposition in accordance with the present invention.

Skilled artisans appreciate that elements in the figures are illustratedfor simplicity and clarity and have not necessarily been drawn to scale.For example, the dimensions of some of the elements in the figures maybe exaggerated relative to other elements to help improve theunderstanding of the embodiments of the present invention.

DETAILED DESCRIPTION

Illustrated in FIG. 1 is a semiconductor device 10 having a metalstructure. Semiconductor device 10 has a substrate 12 and an overlyinginsulating layer 14. The substrate may be of various materials such assilicon or silicon germanium. Other substrate materials may be used. Theinsulating layer 14 may be formed of any type of dielectric material.Common materials used for insulating layer 14 are some form of an oxidesuch as silicon dioxide. Etched within the insulating layer 14 is atrench or via formed by conventional photolithography techniques. Alongthe edges of the trench is formed a thin barrier layer 16. Electrolyticdeposition is used to deposit a metal interconnect 18 over and along allexposed surfaces of the thin barrier layer 16 and to completely fill thetrench or via. In one form, the thin barrier layer 16 is a nitridelayer, but may be any of other materials used as a barrier insemiconductor processing. Typically, the metal interconnect 18 isdeposited to overlie the planar upper surface of the insulating layer 14and chemical mechanical polished (CMP) to a planar upper surface that iscoplanar with the upper surface of the insulating layer 14. The metalthat is used as metal interconnect 18 may be any of a variety of metalssuch as cobalt, tungsten, copper, etc. or a combination thereof.

Illustrated in FIG. 2 is further processing of semiconductor device 10.A barrier layer 20 is formed overlying the metal interconnect 18. In oneform, the barrier layer 20 is for example a cobalt tungsten boron alloy,CoWB. Semiconductor device 10 is merely representative of a number ofmetal deposition applications commonly required in semiconductormanufacturing. In the immediate example, further processing above theinsulating layer 14 and the thin barrier layer 16 is implemented. Suchfurther processing requires annealing of the semiconductor device 10.The application of heat could cause the metal interconnect 18 to diffuseinto overlying materials and into the insulating layer 14 if the barrierlayer 16 and barrier layer 20 were not present. The use of electrolessdeposition of metal therefore is a critical aspect in the manufacture ofa semiconductor. It should also be appreciated that other examples ofmetal deposition by electroless deposition are common. For example, thedeposition of metal layers to form conductors such as power and signalconductors is common.

Illustrated in FIG. 3 is a manufacturing apparatus 30 to manufacture asemiconductor using electroless metal deposition. A reservoir 32 isprovided with an electroless solution or bath solution 34. Above thebath solution 34 is an air region 35. A wafer processing chamber 36 isconnected to the reservoir 32 via an inlet line 40 and an outlet line42. Within the wafer processing chamber 36 is a bath solution 38 inwhich the semiconductor device 10 is immersed. Semiconductor device 10is typically in the form of a semiconductor wafer containing manyindividually integrated circuit devices that are subsequently separatedand packaged individually. A valve 44 is placed in the inlet line 40 anda valve 46 is placed in the outlet line 42. Valve 44 and valve 46 arecontrolled either manually or automatically by control signals (notshown) to transfer the solution between reservoir 32 and the waferprocessing chamber 36. It should also be understood that pumps (notshown) may be included within inlet line 40 and outlet line 42 forimplementing the flow of bath solution 34 and bath solution 38,respectively. In one form, wafer processing chamber 36 is filled andthen periodically circulated back into reservoir 32 and thenreplenished. In yet another form, bath solution 34 and bath solution 38are continuously circulated between the respective containers. Alsoconnected to the reservoir 32 is an analysis module 48. A sampling line54 is connected from within the bath solution 34 to the analysis module48 via a valve 58. A replenishing line 56 is connected to areplenishment module 50. Within the replenishing line 56 is a valve 60.Within the replenishment module 50 is a replenishment solution 52. Whenneeded to adjust bath level, a quantity of the bath solution may beremoved from reservoir 32 through a drain line 62. Within the drain line62 is a valve 64. Drain line 62 is directed as waste to an acceptablewaste storage (not shown). An output of the analysis module 48 is acontrol signal 59 that is connected to a control input of valve 60 forcontrolling whether valve 60 is open or closed. When valve 60 is open,the replenishment solution 52 is coupled into the bath solution 34. Inone form, the replenishment solution 52 is additional reducing agentthat is dissolved in liquid form. For example, in one form thereplenishment solution 52 is morpholine borane dissolved in water inaddition to optional additional components such as a metal, chelatingagents, etc.

In operation, a predetermined bath solution 34 is placed within thereservoir 32. Within the bath solution 34 is at least a predeterminedamount of cobalt salt (CoSO₄ or CoCl₂ for example) and a reducing agent.It should be well understood that other metal salts may be used.Additionally, other components may be added to the bath solution 34 forfunctions such as chelating and pH adjustment. There are numerousacceptable reducing agents that are used in electroless metaldeposition. In one form, the reducing agent MPB (morpholine borane) orDMAB (Dimethylamineborane) may be used. Other reducing agents such ashydrazine, borohydride and hypophosphite may be used. Conventionalcomponent concentrations have a large excess concentration of metal ascompared with the reducing agent. The percentages of metal and reducingagent may vary within well known ranges and will therefore not bespecified herein.

A sample of the bath solution 34 is either continuously fed orperiodically fed to the analysis module 48 in response to controllingvalve 58. When needed, bath solution 34 may be drained from reservoir 32through drain line 62 in response to controlling valve 64, in order tomaintain a liquid optimum level in reservoir 32. In an alternative form,it should be understood that the analysis performed by analysis module48 may be implemented separate and remote from the reservoir 32 and thewafer processing chamber 36 without using sampling lines. The analysismodule 48 functions to drive the metal reduction reaction in the sampleremoved from reservoir 34 to completion and thereby consume allavailable reducing agents. This method allows this process to occurwithin a matter of minutes allowing real time feedback of the solutionchemistry modification. The reduction reaction (driven to completion)generates hydrogen gas in a specific proportion to the original reducingagent concentration.

Illustrated in FIG. 4 is a graph illustrating the relationship ofhydrogen generated during the reduction reaction in the bath solution 34sampled from reservoir 32 to the reducing agent concentration. Therelationship is substantially linear over the process range of concern.As the reducing agent concentration increases, the hydrogen generatedincreases. This relationship may be advantageously used to determine theconcentration of reducing agent. In the example below, the quantity ofhydrogen will be measured in order to determine the concentration of thereducing agent.

The quantity of generated hydrogen gas is either measured as a functionof pressure in a constant volume mode or is measured as a function ofvolume in a constant pressure mode. From this measurement the originalconcentration of reducing agent is determined and one of three possibleactions is implemented in response. The first action is to fully replacethe bath solution 34 and bath solution 38 when the reducing agentconcentration falls below a critical level eliminating the possibilityof reduction reaction byproduct contamination on the plating process.Below this critical level of reducing agent concentration, the metaldeposition will be reduced to an unacceptable level. The second possibleaction is to replenish the level of reducing agent to the normalprocessing level with optional chemical filtration of accumulatedreduction reaction byproducts. In an alternative form, the bath solution34 and bath solution 38 may be partially replaced with fresh solution inorder to replenish the reducing agent concentration and reduce thebyproduct contamination below the level in which it affects the qualityof the deposited metal film. The third option is to adjust the metaldeposition time to compensate for the reduced deposition rate, due tothe lowered reducing agent concentration in order to yield the desiredmetal layer thickness.

Illustrated in FIG. 5 is one form of the evolved hydrogen analysisequipment that may be used to determine the amount of hydrogen generatedby the bath solution 34 sample from reservoir 32 when the reductionreaction is forced to completion by base addition (e.g. hydroxideaddition in one form), consuming all of the available reducing agent.When a reducing agent of DMAB is used, another technique to forcereduction reaction completion is to elevate the temperature of thesampled bath solution. In addition, a combination of pH adjustment andtemperature adjustment may be used to force and accelerate the reactioncompletion. In FIG. 5, a physical principle of using a constant pressureand measuring the volume of hydrogen that is generated is used. Anultrasonic bath 73 is provided with a solution bath sample 72 containedin a vessel. It should be appreciated that other forms of agitationrather than an ultrasonic bath may also be used. The solution bathsample 72 contains the solution sampled from reservoir 32. As noted inFIG. 5, this sample contains, in one form, the basic addition of ahydroxide such as KOH, potassium hydroxide, to create a basic pH ofpreferably about twelve or greater. The agitation causes the rapidcoalescence of generated hydrogen bubbles. The gas hydrogen bubbles arepassed through a tube that is placed in the vessel 74 containing water78 or other liquid capable of forming a gas tight seal with closed-endtube 76. The closed-end tube 76 is originally filled to a knownpredetermined volume at the start of the analysis with water 80 or othersuitable liquid that was contained in vessel 74. The hydrogen gasbubbles accumulate in the upper end of the closed-end tube 76 to form aregion 82 within closed-end tube 76 made up of the evolved hydrogen fromthe reaction in the solution bath 72. The accumulation of hydrogen gasbubbles forces a displacement of water in the vessel 74 and thecollected volume is measured at the end of the analysis by taking thedifference between the initial and final liquid levels in closed-endtube 76. This difference is illustrated in FIG. 5 as delta V, volume.The amount of changed volume within the closed end tube 76 is the sameas the amount of resulting changed volume within vessel 74. The reducingagent concentration of the bath solution 34 is then determined byreferencing this changed volume, delta V, to FIG. 4.

Illustrated in FIG. 6 is yet another form of the hydrogen analysisequipment that may be used to determine the amount of hydrogen generatedby the bath solution sample from reservoir 32 when the reductionreaction is forced to completion by base addition (e.g. hydroxideaddition in one form), consuming all of the available reducing agent. InFIG. 6, a physical principle of using a constant volume and measuringthe pressure of hydrogen that is generated is used. In the illustratedexample, a vessel 92 contains a sample of the bath solution 34. Thevessel 92 is filled in such a manner such as to produce a minimal amountof a head space 96. When the reduction reaction is forced to completion,hydrogen gas is evolved and pressurizes the fixed volume of head space96. The pressure generated within the head space 96 is measured by apressure transducer 94 and is directly related to the quantity ofhydrogen generated and the original reducing agent concentration maythen be determined using a calibration chart similar to that illustratedin FIG. 4.

Illustrated in FIG. 7 is a flowchart of one form of electroless metaldeposition in a semiconductor process according to the presentinvention. A start step 100 initiates the processing. In a step 102semiconductor wafers are placed in a bath solution to be plated with apredetermined metal by an electroless metal deposition. In a step 104 asample of the bath solution is drawn from the bath or vessel containingthe bath solution. In a step 106, the pH of the sample that was drawn isincreased to force the reduction reaction rapidly to completion,generating hydrogen gas from the solution sampled from the bath. Thesample is made more basic by the addition of a hydroxide. In otherforms, reduction reaction is accelerated by raising the temperature ofthe sample or by both the addition of a hydroxide and raising thetemperature.

In a step 108 a change in pressure or volume is measured by using thegenerated hydrogen and a conventional principle of physics. For example,the apparatus of either FIG. 5 or FIG. 6 may be used to measurerespectively a change in volume and pressure. In a step 110 the measuredchange in pressure or volume is used to determine a correlatedconcentration of the reducing agent present in the sample of the bathsolution. In one form, this correlation is made using a graphicalrelationship such as the graph of FIG. 4. How this correlation is mademay vary. For example, the correlation may be done manually butpreferably is performed automatically by software. The correlated valuesmay be stored in a memory (not shown) in order to automate step 110. Ina step 112 various modifications to the main bath solution are madebased on the result of step 110. For example, in step 112 if the valuedetermined in step 110 is below a predetermined critical value the bathsolution of the electroless deposition solution may be partially orfully replaced. Modification of the bath solution may be made by addingmore reducing agent if required. If the concentration of reducing agentcomponent indicated in step 110 is within an acceptable range, no actionmay be needed. Additional actions within step 110 include the adjustmentof deposition time. If the reducing agent component is lower thanearlier in time, rather than change the bath solution component it canbe recognized that the deposition rate is slower and thereforeadditional deposition time may be allowed to complete metal formation.Additionally, if the reducing agent component is lower than earlier intime, rather than change the bath solution component the bath solutionchamber temperature may be elevated. A rise in temperature in the vesselcontaining the bath solution may stimulate the electroless reaction andimprove the deposition rate. A combination of adjusting both the timefor deposition and the vessel temperature may be utilized. After anappropriate action is taken to modify or replace the bath solution, theprocess returns to the beginning of step 102 and the method repeats toplate new wafers.

By now it should be appreciated that there has been provided a methodfor metal plating. A sample of plating solution has the pH thereofadjusted to accelerate a rate of reaction. Gasometric analysis ofevolved or liberated hydrogen is performed to determine a measurement ofthe quantity of hydrogen evolved from the sample. An amount of reducingagent in the sample is determined by a predetermined correlation withthe evolved quantity of hydrogen. In response to knowing theconcentration of reducing agent in the sample, various actions may betaken to the electroless bath solution. The analysis module 48 may beimplemented fully automated with software or may be performed by aseries of steps by an operator of the plating apparatus. Additionally,the calculations and measurements by be automated fully or be performedby a mix of computer automation and manual steps. The method disclosedherein functions to minimize the premature disposal of plating solution,thereby saving significant environmental disposal or recycling expenseassociated with the chemicals involved in a plating process.

There is provided herein a method for making a semiconductor device. Adevice structure is provided having an active circuit region and a metalinterconnect that is over and insulated from the active circuit region.The metal interconnect has a top surface that is exposed. A plating bathhaving a reducing agent is provided. A sample of the plating bath isobtained. The pH of the sample is increased. A quantity of hydrogenevolved from the sample is measured. The quantity of hydrogen measuredis used to determine a concentration of the reducing agent present inthe sample. The top surface of the metal interconnect is plated byimmersing the device structure in the plating bath if the concentrationof the reducing agent is within a predetermined range. In one formincreasing the pH is performed by adding a hydroxide to the sample. Inanother form the interconnect is at least copper and the platingincludes forming a layer of an alloy of cobalt on the top surface. Inanother form the reducing agent is morpholine borane. In another formthe reducing agent is characterized as producing hydrogen gas during areduction reaction. In another form the reducing agent is characterizedas having a reducing rate that occurs more rapidly with an increase inpH. In another form the step of measuring the quantity of evolvedhydrogen includes providing an expandable space at a substantiallyconstant pressure and directing hydrogen evolved from the sample intothe expandable space. A change in the expandable space is measured andthe quantity of hydrogen is determined based on the change in expandablespace. In another form the expandable space is bounded by a containerand a liquid at atmospheric pressure. In another form the step ofmeasuring the quantity of hydrogen includes providing a space ofconstant volume and directing hydrogen evolved from the sample into thespace of constant volume. A change in pressure in the space of constantvolume is measured. The quantity of hydrogen is determined based on thechange in pressure in the space of constant volume. In one form thespace of constant volume is bounded by a container and the sample. Inanother form turbulence is created in the sample. In one form turbulenceis created by sonicating. In another form the plating bath is replacedif the concentration of the reducing agent is not within thepredetermined range. In another form a quantity of reducing agent isadded to the plating bath to obtain a modified plating bath if theconcentration of the reducing agent is below a predetermined level. Inanother form the bath is partially replaced with fresh bath solution toboth increase the reducing agent concentration and reduce the level ofreaction byproduct contamination. In another form the top surface of themetal interconnect is plated by immersing the device structure in themodified plating bath. In yet another form plating the top surface isperformed for a period of time based on the concentration of thereducing agent.

In yet another form there is provided a device to be plated. A platingbath having a reducing agent is provided. A sample of the plating bathis obtained. The pH of the sample is increased. A quantity of hydrogenevolved from the sample is measured. The quantity of hydrogen measuredis used to determine a concentration of the reducing agent present inthe sample. The device is plated by immersing the device in the platingbath if the concentration of the reducing agent is within apredetermined range. In one form the pH is increased by adding potassiumhydroxide to the sample. In another form the reducing agent is one ofhypophosphite, morpholine borane, dimethylamineborine, borohydride orhydrazine. In another form the quantity of hydrogen is measured byproviding an expandable space at a constant pressure. Hydrogen evolvedfrom the sample is directed into the expandable space. A change in theexpandable space is measured. The quantity of hydrogen is measured basedon the change in expandable space. In yet another form the quantity ofhydrogen is measured by providing a space of constant volume. Hydrogenevolved from the sample is directed into the space of constant volume. Achange in pressure in the space of constant volume is measured. Thequantity of hydrogen is measured based on the change in pressure in thespace of constant volume. In one form the sample is sonicated.

In another form the plating bath is replaced if the concentration of thereducing agent is not within the predetermined range. In another formreducing agent is added to the plating bath to obtain a modified platingbath if the concentration of the reducing agent is below a predeterminedlevel. The device is plated by immersing the device structure in themodified plating bath. In another form plating the device is performedfor a period of time based on the concentration of the reducing agent.

In yet another form there is provided an electroless plating apparatus.A plating container includes a plating bath having a reducing agent. Ananalysis module is provided for determining a concentration of thereducing agent of a sample of the plating bath by increasing the pH ofthe sample and measuring a quantity of hydrogen evolved from the sample.In one form the analysis module sonicates the sample. In another formthe analysis module adds a hydroxide to increase the pH of the sample.In yet another form the analysis module measures the quantity ofhydrogen evolved from the sample as an increase in volume of anexpandable space that receives the hydrogen. In another form theanalysis module measures the quantity of hydrogen evolved from thesample as an increase in pressure in a space of fixed volume thatreceives the hydrogen that is evolved from the sample. In one form thereducing agent is morpholine borane. In another form a second containerof reducing agent is coupled to the analysis module and the platingcontainer. The second container supplies reducing agent to the platingbath to increase the concentration of reducing agent in the plating bathas indicated as needed by the analysis module.

In yet another form there is provided a method of making a semiconductordevice. A device structure having an active circuit region and a metalinterconnect that is over and insulated from the active circuit regionis provided. The metal interconnect has a top surface that is exposed. Aplating bath is provided having one of morpholine borane ordimethylamineborane as a reducing agent. A sample of the plating bath isobtained. Potassium hydroxide is introduced into the sample to assist indriving a reduction reaction, involving the reducing agent, tocompletion. A quantity of hydrogen evolved from the reduction reactionis measured to determine a concentration of the reducing agent presentin the sample. The top surface of the metal interconnect is plated byimmersing the device structure in the plating bath if the concentrationof the reducing agent is determined to be within a predetermined range.

In the foregoing specification, the invention has been described withreference to specific embodiments. However, one of ordinary skill in theart appreciates that various modifications and changes can be madewithout departing from the scope of the present invention as set forthin the claims below. For example, while the plating of a semiconductordevice is disclosed herein, it should be apparent that items other thana semiconductor device may be plated. Various metals may be used inconnection with the disclosed deposition process. Various platingsolutions having differing chemical compositions may be used, such asvarious reducing agents.

Accordingly, the specification and figures are to be regarded in anillustrative rather than a restrictive sense, and all such modificationsare intended to be included within the scope of the present invention.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any element(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature or element of any or all the claims. As used herein, the terms“comprises,” “comprising,” or any other variation thereof, are intendedto cover a non-exclusive inclusion, such that a process, method,article, or apparatus that comprises a list of elements does not includeonly those elements but may include other elements not expressly listedor inherent to such process, method, article, or apparatus. The terms aor an, as used herein, are defined as one or more than one. The termplurality, as used herein, is defined as two or more than two. The termanother, as used herein, is defined as at least a second or more. Theterms including and/or having, as used herein, are defined as comprising(i.e., open language). The term coupled, as used herein, is defined asconnected, although not necessarily directly, and not necessarilymechanically.

1. A method of making a semiconductor device, comprising: providing adevice structure having an active circuit region and a metalinterconnect that is over and insulated from the active circuit region,wherein the metal interconnect has a top surface that is exposed;providing a plating bath having a reducing agent; obtaining a sample ofthe plating bath; increasing pH of the sample; measuring a quantity ofhydrogen evolved from the sample; using the quantity of hydrogenmeasured in the step of measuring to determine a concentration of thereducing agent present in the sample; and plating the top surface of themetal interconnect by immersing the device structure in the plating bathif the concentration of the reducing agent is within a predeterminedrange.
 2. The method of claim 1, wherein the step of increasing the pHcomprises adding a hydroxide to the sample.
 3. The method of claim 1,wherein the metal interconnect comprises copper and the step of platingcomprises forming a layer of an alloy of cobalt on the top surface. 4.The method of claim 1, wherein the reducing agent comprises morpholineborane.
 5. The method of claim 1, wherein the reducing agent ischaracterized as producing hydrogen gas during a reduction reaction. 6.The method of claim 5, wherein the reducing agent is characterized ashaving a reducing rate that occurs more rapidly with an increase in pH.7. The method of claim 1, wherein the step of measuring the quantity ofhydrogen comprises: providing an expandable space at a substantiallyconstant pressure; directing hydrogen evolved from the sample into theexpandable space; measuring a change in the expandable space; anddetermining the quantity of hydrogen based on the change in expandablespace.
 8. The method of claim 7, wherein the expandable space is boundedby a container and a liquid at atmospheric pressure.
 9. The method ofclaim 1, wherein measuring the quantity of hydrogen, comprises:providing a space of constant volume; directing hydrogen evolved fromthe sample into the space of constant volume; measuring a change inpressure in the space of constant volume; and determining the quantityof hydrogen based on the change in pressure in the space of constantvolume.
 10. The method of claim 9, wherein the space of constant volumeis bounded by a container and the sample.
 11. The method of claim 1further comprising creating turbulence in the sample.
 12. The method ofclaim 11 wherein creating turbulence comprises sonicating the sample.13. The method of claim 1, further comprising: replacing part or all ofthe plating bath if the concentration of the reducing agent is notwithin the predetermined range.
 14. The method of claim 1, furthercomprising: adding a quantity of reducing agent to the plating bath toobtain a modified plating bath if the concentration of the reducingagent is below a predetermined level; and plating the top surface of themetal interconnect by immersing the device structure in the modifiedplating bath.
 15. The method of claim 1, wherein the step of plating thetop surface is performed for a period of time based on the concentrationof the reducing agent.
 16. A method of plating, comprising: providing adevice to be plated; providing a plating bath having a reducing agent;obtaining a sample of the plating bath; increasing a pH of the sample;measuring a quantity of hydrogen evolved from the sample; using thequantity of hydrogen measured in the step of measuring to determine aconcentration of the reducing agent present in the sample; and platingthe device by immersing the device in the plating bath if theconcentration of the reducing agent is within a predetermined range. 17.The method of claim 16, wherein the step of increasing the pH comprisesadding potassium hydroxide to the sample.
 18. The method of claim 16,wherein the reducing agent comprises one of hypophosphite, morpholineborane, dimethylamineborine, borohydride or hydrazine.
 19. The method ofclaim 16, wherein the step of measuring the quantity of hydrogencomprises: providing an expandable space at a constant pressure;directing hydrogen evolved from the sample into the expandable space;measuring a change in the expandable space; and determining the quantityof hydrogen based on the change in expandable space.
 20. The method ofclaim 16, wherein the step of measuring the quantity of hydrogen,comprises: providing a space of constant volume; directing hydrogenevolved from the sample into the space of constant volume; measuring achange in pressure in the space of constant volume; and determining thequantity of hydrogen based on the change in pressure in the space ofconstant volume.
 21. The method of claim 16 further comprisingsonicating the sample.
 22. The method of claim 16, further comprising:replacing all or part of the plating bath if the concentration of thereducing agent is not within the predetermined range.
 23. The method ofclaim 16, further comprising: adding reducing agent to the plating bathto obtain a modified plating bath if the concentration of the reducingagent is below a predetermined level; and plating the device byimmersing the device in the modified plating bath.
 24. The method ofclaim 16, wherein the step of plating the device is performed for aperiod of time based on the concentration of the reducing agent.
 25. Anelectroless plating apparatus, comprising: a plating containercomprising a plating bath having a reducing agent; and an analysismodule that determines a concentration of the reducing agent of a sampleof the plating bath by increasing a pH of the sample and measuring aquantity of hydrogen evolved from the sample.
 26. The electrolessplating apparatus of claim 25, wherein the analysis module is furthercharacterized as sonicating the sample.
 27. The electroless platingapparatus of claim 25, wherein the analysis module is furthercharacterized adding a hydroxide to increase the pH of the sample. 28.The electroless plating apparatus of claim 25, wherein the analysismodule is further characterized as measuring the quantity of hydrogenevolved from the sample as an increase in volume of an expandable spacethat receives the hydrogen.
 29. The electroless plating apparatus ofclaim 25, wherein the analysis module is further characterized asmeasuring the quantity of hydrogen evolved from the sample as anincrease in pressure in a space of fixed volume that receives thehydrogen that is evolved from the sample.
 30. The electroless platingapparatus of claim 25, wherein the reducing agent is morpholine borane.31. The electroless plating apparatus of claim 25 further comprising asecond container of reducing agent, coupled to the analysis module andthe plating container, that supplies reducing agent to the plating bathto increase the concentration of reducing agent in the plating bath asindicated as needed by the analysis module.
 32. A method of making asemiconductor device, comprising: providing a device structure having anactive circuit region and a metal interconnect that is over andinsulated from the active circuit region, wherein the metal interconnecthas a top surface that is exposed; providing a plating bath having oneof morpholine borane or dimethylamineborane as a reducing agent;obtaining a sample of the plating bath; introducing potassium hydroxideinto the sample to assist in driving a reduction reaction, involving thereducing agent, to completion; measuring a quantity of hydrogen evolvedfrom the reduction reaction to determine a concentration of the reducingagent present in the sample; and plating the top surface of the metalinterconnect by immersing the device structure in the plating bath ifthe concentration of the reducing agent is within a predetermined range.33. The method of claim 32, wherein the step of measuring the hydrogencomprises: providing an expandable space at a constant pressure;directing the hydrogen evolved from the sample into the expandablespace; and measuring a change in the expandable space to determine theconcentration of the reducing agent.
 34. The method of claim 32, whereinthe step of measuring the quantity of hydrogen, comprises: providing aspace of constant volume; directing hydrogen evolved from the sampleinto the space of constant volume; and measuring a change in pressure inthe space of constant volume to determine the concentration of thereducing agent.
 35. The method of claim 32 further comprising sonicatingthe sample.
 36. The method of claim 32, further comprising: replacingthe plating bath if the concentration of the reducing agent is notwithin the predetermined range.
 37. The method of claim 32, furthercomprising: adding reducing agent to the plating bath to obtain amodified plating bath if the concentration of the reducing agent isbelow the predetermined range; and plating the semiconductor device byimmersing the device structure in the modified plating bath.
 38. Themethod of claim 32, wherein the step of plating the semiconductor deviceis performed for a period of time based on the concentration of thereducing agent.